The present invention relates to a radiological imaging apparatus, and more particularly, to a radiological imaging apparatus ideally applicable to radiological two-dimensional image pickup apparatus, X-ray computed tomography (hereinafter referred to as “X-ray CT”), positron emission computed tomography (hereinafter referred to as “PET”) and single photon emission computed tomography (hereinafter referred to as “SPECT”).
Among typical radiological imaging apparatuses, which is a non-invasive imaging technology for examining functions and conformation of the body of a medical examinee, are radiological two-dimensional image pickup apparatus, X-ray CT, PET and SPECT, etc.
PET inspection is an inspection consisting of administering radiopharmaceutical (hereinafter referred to as “PET radiopharmaceutical”) including positron emitters (15O, 13N, 11C, 18F, etc.) to the examinee and examining locations in the body where more PET radiopharmaceutical is consumed. The PET inspection is an action of detecting γ-rays emitted from the body of the examinee caused by PET radiopharmaceutical using a radiation detector. More specifically, one positron emitted from a positron emitter in the PET radiopharmaceutical couples with an electron of a neighboring cell (cancerous cell), disappears and at the same time irradiates a pair of γ-rays (called “γ-ray pair”) having energy of 511 keV. These γ-rays are emitted in directions opposite to each other (180°±0.6°). Detecting this pair of γ-rays using a radiation detector makes it possible to know between which pair of radiation detectors the positron is emitted. Detecting those many γ-ray pairs makes it possible to identify locations where more PET radiopharmaceutical is consumed. For example, when PET radiopharmaceutical created by coupling positron emitters and carbohydrate is used, it is possible to discover cancer focuses having hyperactive carbohydrate metabolism. One example of the radiological imaging apparatus used for PET is described in JP-A-7-20245. The data obtained is converted to data of each voxel using the Filtered Back Projection method described in non-patent document 1 (IEEE Transaction on Nuclear Science, Vol. NS-21, pp. 228–229). Positron emitters (15O, 13N, 11C and 18F, etc.) used for the PET inspection have a half life of 2 to 110 minutes.
The SPECT administers radiopharmaceutical (hereinafter referred to as “SPECT radiopharmaceutical”) including single photon emitters (99Tc, 67Ga, 201Tl, etc.) and matters (e.g., carbohydrate) having a property of concentrating on a specific tumor or specific molecule to an examinee and detects γ-rays emitted from the emitters using a radiation detector. The energy of γ-rays emitted from the single photon emitters often used for inspection using the SPECT is around several 100 keV. In the case of the SPECT, single γ-rays are emitted, and therefore it is not possible to obtain their angle of incidence upon the radiation detector. Thus, angle information is obtained by detecting only γ-rays incident from a specific angle through a collimator using the radiation detector. The SPECT is an inspection method of identifying locations where more SPECT radiopharmaceutical is consumed by detecting γ-rays generated in the body caused by the SPECT radiopharmaceutical. One example of the radiological imaging apparatus used for the SPECT is described in JP-A-9-5441. The SPECT also converts data obtained to data of each voxel using a method such as Filtered Back Projection. The SPECT may also take transmission images. 99Tc, 67Ga and 201Tl used for the SPECT have a half life longer than that of radionuclide used for the PET, for example, 6 hours to 3 days.